Interface Collect

aiscript-arena/src/collect.rs:23–40

A trait for garbage collected objects that can be placed into `Gc` pointers. This trait is unsafe, because `Gc` pointers inside an Arena are assumed never to be dangling, and in order to ensure this certain rules must be followed: 1. `Collect::trace` *must* trace over *every* `Gc` pointer held inside this type, and cannot fail. 2. Held `Gc` pointers must not be accessed inside `Drop::drop` since

/// while ensuring that the write barrier is always executed.
/// # Safety
pub unsafe trait Collect {
    /// As an optimization, if this type can never hold a `Gc` pointer and `trace` is unnecessary
    /// to call, you may implement this method and return false. The default implementation returns
    /// true, signaling that `Collect::trace` must be called.
    #[inline]
    fn needs_trace() -> bool
    where
        Self: Sized,
    {
        true
    }

    /// *Must* call `Collect::trace` on all held `Gc` pointers. If this type holds inner types that
    /// implement `Collect`, a valid implementation would simply call `Collect::trace` on all the
    /// held values to ensure this.
    #[inline]
    fn trace(&self, _cc: &Collection) {}
}